You can use Bessel filters to reduce nonlinear-phase distortion inherent in all IIR filters. High-order IIR filters and IIR
filters with a steep roll-off have a pronounced nonlinear-phase distortion, especially in the transition regions of the filters.
You also can obtain linear-phase response with FIR filters.

The following figure shows the magnitude and phase responses of a lowpass Bessel filter.

In the previous figure, the magnitude is smooth and monotonically decreasing at all frequencies.

The following figure shows the phase response of a lowpass Bessel filter.

The previous figure shows the nearly linear phase in the passband. Also, the phase monotonically decreases at all frequencies.